1. Field of the Invention
The invention relates to the field of automated pipettes. In still greater particularity the invention relates to an automated pipette employing a device to ensure full volume pickup. By way of further characterization but not by way of limitation thereto, the invention is an automated pipette with optical detectors to sense the presence of a liquid within the pipette.
2. Description of the Related Art
Many measuring and testing instruments as, for example, immunonephelometric instruments such as that described in U.S. Pat. No. 4,157,871 issued on June 12, 1979, require successive manipulations of the sample substance to be tested. These manipulations consume a great deal of operator time when a number of assays on many samples are performed. To obtain good results, an operator must repeat a number of steps in the proper sequence for each sample. Manual pipetting steps include the identification of a number of samples and may require exact volume pickup. Because the sample manipulations are usually done by hand, operator fatigue and boredom too often result in erroneous results. Additionally, the reduction in operator morale due to fatigue and boredom generally contributes to a decrease in job performance resulting in increased operating costs for the laboratory. In addition, where exact volumes are required to be used, operator error, however slight, may cause inconsistent or erroneous results.
Of major importance in sample handling technique is preciseness in the amount of substance, either sample, diluent, or reagent which must be taken to assure accurate, reproducible results. Failure in sample quantity preciseness can become a major problem in any assay protocol. This problem may occur during manual as well as automated sample handling. For example, an operator, during manual pipetteting, may take slightly more or less of the substance than is required. Reading of the meniscus, tilting of the pipette, and similar factors may result in measuring errors. Accuracy thus depends on the degree of intuitive skill or carefulness of the operator. With an automated pipette the motions of the hardware are very well defined and volume displacement is standardized to avoid careless errors. However, the accuracy of incremental measurements depends upon transferring exact volumes and it is important to know that the desired volume has been transferred. With robot motions of a pipette the depth of penetration into the liquid container is well defined. However, if the solution level drops below the pickup tip position, it is possible to pick up an incomplete volume. During manual operation a technician may lower the tip further to pick up a greater volume. In an automated system a robot cannot easily make this decision.